Grace is the Pierson family cat, and David's feline companion through time. A few years before the book began, she kept following David, claiming him as her human.
When the family moves to the farmhouse at Beak's End, Grace picks up on the ghost of Nathaniel Ley, as shown when she hisses.
One night when the paranormal activity in the farmhouse goes through the stratosphere, Grace jumps out the window. At the little bridge, Cecilia finds Grace and calms her down.
Grace is fond of Cecilia, and recognizes her when she sees her as Lia Bailey.